The present invention relates to an improved biocatalytic process for the preparation of phenolic resins using soybean peroxidase and more generally to a biocatalytic process for oxidizing phenols and other compounds using soybean peroxidases.
The present invention further relates to a method for treating peroxidase enzymes so that they may be used in applications where the untreated enzyme could not previously be employed. More particularly, it relates to a method for treating a peroxidase enzyme source with a purifying agent to reduce the amount of impurities in the enzyme and thereby reduce contamination in processes using such enzymes as a biocatalyst.
U.S. Pat. No. 4,900,671 commonly assigned to the Mead Corporation discloses a method for preparing a phenolic resin which comprises preparing a solution of a phenol in a water miscible or immiscible solvent and an aqueous solution of a peroxidase or oxidase enzyme, mixing the two solutions and adding a peroxide or oxygen. The preferred method described in this patent makes use of horseradish peroxidase. The reaction is preferably carried out in a mixed solvent system. The peroxidase is dissolved in water, the phenol is dissolved in a solvent which may be water miscible or water immiscible. Hydrogen peroxide is added to the system and reaction occurs on the enzyme. It has now been found that soybean peroxidase is much more economical to use in this method. It has also been found that the quality of resin obtained from this method can be improved if the peroxidase is treated as described herein.
Alberti and Klibanov, BIOLOGICAL DETOXICATION, Chapter 22, Peroxidase for Removal of Hazardous Aromatics from Industrial Wastewaters, (1982), discloses that phenols can be removed from wastewaters as high molecular weight polymers by the action of peroxidase enzymes. The disclosed method relies on the ability of peroxidase enzyme to catalyze, with hydrogen peroxide, the oxidation of a variety of phenols and aromatic amines. Phenolic and aromatic amine free radicals are generated, which diffuse from the active center of the enzyme into solution, and polymerize to polyaromatic products. These high molecular weight polymers are water-insoluble and can be readily separated by filtration from water.
In the past, peroxidase enzymes have not been available at a cost and in a purity amenable to many biocatalytic processes. For example, horseradish roots, a common source of horseradish peroxidase, are cultivated generally in small quantities and are propagated through root cuttings, thus making it difficult to scale up production. The limited availability of the horseradish root extract coupled with the shortage of alternative sources of enzyme has created a very expensive market for such enzymes. Accordingly, there exists in the marketplace a need for an abundant and relatively inexpensive source of peroxidase.